The invention relates to a contact tip for a welding and cutting torch with one or several internal openings for guiding and contacting one or more welding electrodes.
EP 41 165 A1 discloses an inert gas shielded arc welding torch with a contact tip of the aforedescribed type, which is referred therein as a contact tube. This component is attached to the tip of the inert gas shielded arc welding torch and guides the welding electrode to the starting location of the arc. The contact tip also supplies the relatively large welding current to the welding electrode. Due to the large current flow and the high thermal load, the contact tip is highly stressed. For this reason, the contact tip has until now been fabricated of drawn copper material, using an alloy consisting of electrolytic copper and copper-chromium-zirconium in the form of a semi-finished hollow material. The production tools and facilities and the manufacturing process for such drawn materials are quite complex, so that only a small number of suppliers are active in this market which is reflected in correspondingly high material costs. Another disadvantage is that special devices have to be manufactured for each specified nominal diameter and for each required tolerance. This poses a disadvantage in particular with small production runs. Drawn material is particularly disadvantageous since the characteristic material properties may change as a result of the heat treatment and the forming process. The heat treatment and the forming process causes changes in the material characteristics which adversely affect the surfaces and the wear characteristics of the internal opening.
Accordingly, it is an object of the invention to provide a contact tip for welding and cutting torches which can be produced more cost-effectively.
The object is solved by the invention by providing a contact tip which has at least one interior opening produced by deep drilling into the semi-finished product. Contact tips which can also be produced by drilling are known from GB-A 13 59 875, EP 399 344 A2 and the patent abstract of Japan 08 081 723, as far as the fabrication method is disclosed therein. Disadvantageously, however, the drilling process takes a long time and the internal produced surfaces do not have a sufficient accuracy.
Deep drilling is characterized by the use of tools capable of guiding lubricants and drilling fluid to the tip of the drill bit and forcing removal of the chips. Furthermore, deep drilling uses a high drilling speed, i.e., the produced chips are small in size and the drilling operation can run continuously because the chips are continuously removed.
According to a particular feature of this method, the flushing operation operates at an elevated pressure wherein the lubricants and the drilling fluid are guided along the drilling toolxe2x80x94inside a specified groovexe2x80x94to the tip, whereas the produced small drilling chips are removed to the rear. The chips are small enough to flow along the specified groove. In conjunction with specially developed tools and depending on the material, deep drilling can produce an accuracy in the range of IT 6 to IT 9 in a single processing step without subsequent finish treatment.
With the invention, materials can be employed which are significantly cheaper than the conventional materials currently in use. Moreover, materials spanning a large alloy composition range can be selected, so that the entire contact tip can be produced at lower cost. The fabrication process according to the invention is independent of the drawing characteristics of the material so that a greater variety of materials can be employed than is possible with conventional fabrication processes. Accordingly, specific material requirements can be taken into consideration which was not possible until now. For example, materials can be used which cannot be drawn at all or only with great difficulty. Also, materials can be used which cannot be produced at all or only with great difficulty in the form of a hollow profile (nozzle tube). The semi-finished product can be either a solid material or a tubular material.
For example, alloys can now be employed which cover a greater range with respect to the material characteristics, heat treatment, prior forming steps or the material history. Accordingly, a material can be selected which is optimized with respect to wear resistance and current transfer. With the invention, materials or semi-finished products can now be employed which could not be processed using the conventional fabrication process (drawing process). Unlike conventional materials, the semi-finished products made of the alloys according to the invention need no longer be ductile. Alloys can therefore be employed for the contact tips which until now were not deemed suitable for such an application.
Deep drilling also does not significantly affect the properties of the semi-finished products, so that their characteristic properties can be estimated or predetermined, without subsequently undergoing changes. As yet another advantage, the surface quality and the improved tolerances can be attained in a single processing step. With the improved tolerances, the current during the welding operation is transferred in a defined manner across the entire contact tip and the mechanical guiding is improved which in turn reduces the electrical, thermal and also mechanical wear.
Particularly advantageous is the improved manufacturability, since drawn semifinished products are eliminated. Instead, the semi-finished product can consist of simple metal rods in which the necessary opening(s) are later formed by deep drilling.
A contact tip of this type is preferably fabricated by clamping a rod-shaped material which is made of a desired alloy and has a desired outside diameter, in a conventional deep drilling machine and forming the one or several opening(s) in the semi-finished product by deep drilling. Deep drilling also produces a very precise interior surface, wherein the friction coefficient relative to the welding electrode can be accurately predicted and is not subject to variations.
Other objects, advantages, features and applications of the present invention are disclosed in the following a description of an embodiment with reference to the drawings. All described and /or illustrated features, either alone or in combination, form the subject matter of the present invention, independent of their combination or dependence in the claims.